The present invention relates to an improved method and apparatus for non-intrusive detection of electronic signals in conductors; specifically to an improved method and apparatus for detecting the presence, identity, and relative strength of digital carrier signals on telephone cables.
A popular technique for increasing the efficiency of lo telephone signal transmission over a twisted pair transmission line is the use of digital carriers in a multiplexing scheme. The ability to determine which twisted pairs in the telephone cable bundle are carrying digital carrier signals is essential when repairing or modifying such cables. One must be able to make such determination in a non-intrusive manner or telephone service will be interrupted.
Prior art non-intrusive digital carrier signal detection schemes exist but require expensive heterodyning signal processing circuitry or fail to provide any information about the relative strength or identity of the digital carrier. An example of the prior art heterodyning signal processing circuitry is disclosed in Buzbee, U.S. Pat. No. 5,140,614, which requires crystal controlled oscillators and mixing amplifiers which are complex and costly relative to the apparatus of the present invention.
In addition, the Buzbee U.S. Pat. No. 5,140,614 refers, in the background section, to a carrier signal detection apparatus which does not require heterodyning signal processing circuitry, but which fails to provide relative signal strength or signal identity information. The signal on the twisted pair transmission line is obtained by capacitive or inductive coupling and is filtered so as to pass only the carrier signal. This signal is then amplified and if the signal exceeds a threshold level an audio tone is generated. The only information conveyed by the scheme is that the carrier signal has exceeded the threshold level. The relative strength of the signal and the carrier identity are undetectable and remain unknown.
Furthermore, the prior art detection schemes disclosed in Buzbee U.S. Pat. No. 5,140,614 do not disclose conductive signal probes which can detect both digital carrier signals and audible frequency tracing tones, thereby not allowing a particular wire to be traced from one location to another with the same sensing probe that detects whether or not a carrier signal is present.
Accordingly, it is an object of the present invention to provide a cost effective apparatus and method for detecting the presence, the relative strength, and the identity of digital carrier signals on a telephone cable.
It is another object of the invention to provide an apparatus and method for detecting digital carriers on a telephone cable in a non-intrusive manner so as not to degrade or interrupt telephone service being carried on the telephone cable.
Still another object of the present invention is to provide a method and apparatus for detecting both digital carrier signals and audio frequency tracing tones with the same non-invasive probe.